M. Pourakbari-Kasmaei, M. Rashidi-Nejad and A. Abdollahi
Journal of Applied Sciences 9 ( 16 ): 2962 - 2968 , 2009
A. Abdollahi, M.T. Heydari and M. Moosavi
Journal of Mathematics and Statistics 5 ( 4 ): 348 - 351 , 2009